Update python3 sed hack to avoid '/usr/bin/python32' dep
    
    In F28 and earlier /usr/bin/python exists during the build, and
    the build process decides PYTHON is /usr/bin/python, so this
    sed command works. In F29+ /usr/bin/python does not exist during
    the build, so the build process decides /usr/bin/python2 is
    PYTHON, and when we do 's!/usr/bin/python!/usr/bin/python3!', we
    wind up with /usr/bin/python32...which is not what we wanted.
    So, let's fix that.